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How should we treat virtual methods exposed in APIs (Part 2)

In postul precedent am descutat despre o problema care poate sa apara cand expunem intr-un API metode virtuale, care sunt apoi suprascrise de catre un alt dezvoltator. Iar o versiune ulterioara a API schimba comportamentul aplicatiei in asa fel incat suntem obligati sa schimbam codul care foloseste API expus.
Mai jos gasiti o posibila solutie la aceasta problema.
public abstract class FooBase
{
private void DoAction()
{
// Custom code that can be executed by our method.
DoActionCore();
// More custom code that can be executed by our method.
}

public virtual void DoActionCore()
{
// Some action
}
}

public class MyCustomFoo : FooBase
{
public override void DoActionCore()
{
// My custom code of MyCustomFoo that will be
// executed by DoAction method from base class.
}
}
O solutie de acest gen o sa functioneze, doar daca cel care expune API o sa o foloseasca de la prima versiune.
O alta varianta este ca metode DoActionCore sa fie declarata ca si abstracta, in cazul in care vrem sa obligam dezvoltatorul sa defineasca un comportament custom.

Comments

  1. Presupui ca atunci cind un API este creat intr-un anumit fel, el este imutabil pentru ca exista deja third party-uri care il folosesc. Dar de fapt imutabilitatea aceasta nu preclude existenta unei alte variante de API care sa faca ce trebuie.

    In alte cuvinte nu sint de acord cu ideea ca ceva merge doar daca s-a gindit cineva inainte la asta. Orice design trebuie sa fie adaptabil, iar asta este singura responsabilitate a dezvoltatorului: sa il faca astfel.

    ReplyDelete
  2. Solutia asta are si un nume - template method pattern (http://en.wikipedia.org/wiki/Template_method_pattern).

    E ok ca si metoda de a permite customizarea behaviour-ului unei clase cat timp nu apar ierarhii de clase pe mai mult de 2 nivele, si cat timp nu apare necesitatea ca pentru o singura metoda din clasa de baza sa se ofere mai multe puncte de extensie - in ambele cazuri template method (foarte folosit cu ceva ani in urma) duce la cod greu de inteles si de intretinut.

    ReplyDelete
    Replies
    1. Mersi Tudor ca acum pot sa pun titlu la un sablon pe care il cunosteam si foloseam ;)

      Delete
    2. :) e doar o conventie - si eu il foloseam cu 10 ani in urma si nu stiam cum l-au botezat..

      Delete

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